When the semiconductor wafers are manufactured, it is important to quickly start a manufacturing process and to shift to a high-yield mass-production system at an early stage in order to ensure profitability. For this purpose, various inspection/measurement devices are introduced to manufacturing lines.
As a representative inspection device, an optical wafer inspection device is known. For example, JP-A-2000-105203 (PTL 1) discloses a technique for inspecting the defect in such a way that an optical image of a wafer surface is captured using bright field illumination and is compared with an image of a non-defective site (for example, an image of an adjacent chip). However, according to this optical inspection device, a resolution limit of an acquired image is approximately several hundred nanometers due to the influence of the illumination wavelength. Accordingly, it is possible to detect only whether or not the defect is present in the order of several tens of nanometers on the wafer. Consequently, in a case where the defect has to be analyzed in detail, it is necessary to separately provide a defect observation device having higher imaging resolution.
The defect observation device is a device which outputs an image after imaging a defect position on the wafer with high resolution using an output of an inspection device. An observation device using a scanning electron microscope (SEM) (hereinafter, referred to as a review SEM) is widely used. Observation work needs to be automated in mass production lines of semiconductors, and the review SEM is provided with a defect image automatic collection process (ADR: Automatic Defect Review) which automatically collects images at the defect position in a sample. Errors are included in defect position coordinates (coordinate information indicating the defect position on the sample) output by the inspection device. Accordingly, ADR is provided with a function to obtain an observation-purpose image by re-detecting the defect from an image in which the defect position coordinates output by the inspection device are mainly imaged using a wide field of view and by imaging the re-detected defect position at high magnification.
As a defect detection method from an SEM image, an image obtained by imaging a region having a circuit pattern the same as that of a defect site is used as a reference image so that the reference image is compared with an image obtained by imaging the defect site. JP-A-2001-189358 (PTL 2) discloses this method for detecting the defect. In addition, JP-A-2007-40910 (PTL 3) discloses a method for detecting the defect from one image obtained by imaging the defect site. In addition, JP-A-2013-168595 (PTL 7) discloses a method for recognizing a circuit pattern region from a captured image.
Many types of structures are used for the circuit patterns formed on the semiconductor wafer, and the defects appear in various types and at various positions. In order to improve visibility of the circuit patterns having various structures and various types of defects, it is an effective way to cause a plurality of detectors to detect electrons emitted from a sample at different emission angles or with different emission energies. For example, JP-A-2012-186177 (PTL 4) discloses that information on target irregularities can be recognized by detecting and discriminating the electrons generated from the sample, based on an elevation angle and an azimuth angle of the emitted electrons. In addition, JP-A-1-304647 (PTL 5) discloses a method for detecting the defect by using the plurality of detectors arranged by dividing reflected electrons emitted in each direction. In addition, JP-A-2013-232435 (PTL 6) discloses a method for improving a contrast of a lower layer pattern in a multilayer by synthesizing detector images obtained from the plurality of detectors.